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1. Field of the Invention
This invention relates generally to testing of protection systems for electric power lines, transformers, generators, and substation apparatus and more particularly concerns testing of protection and control intelligent electronic devices (IEDs) based on a data exchange using digital communication between the test system and the intelligent electronic devices (IEDs) being tested which eliminates the need for individual point-to-point wiring of the binary input and output status between the IEDs and test system.
2. Description of the Related Art
Electric power systems generally include a generating source, high-voltage transmission lines and a lower voltage distribution network for delivery of electric power to customers. The apparatus and components of the electric power system are typically monitored with a number of protection relays, protection devices, and meters that determine, among other tasks, where and when a fault occurs in the power system. These protective relays and devices isolate the fault and maintain power system integrity by controlling the power system apparatus, typically circuit breakers and switches with open (trip) or close command signals.
Protective relays historically are mechanical, electromechanical, or solid-state in design, being single-function protective devices, and provide no data communication capabilities. Each single-function protective device is used to detect a specific power system problem by typically monitoring a combination of voltage/current waveforms and/or the power system apparatus status and based on a threshold setting toggle a relay contact close/open (1 or 0 respectively) indicating that logical threshold detection. By grouping multiple single-function protection devices, more complex protection logic can be provided to precisely control the apparatus of the electric power system.
Using prior art, testing these single-function protection devices required a test system for generation of analog outputs that typically included voltage and current waveforms which simulated the electric power system condition that the protection device was designed to detect. Simultaneously, the protection device was monitored via an output contact (as an input to the test system) to determine the proper detection of the simulated condition. Additionally, the test system provided a contact output to simulate the power system apparatus status which was synchronized to the simulation as an input to the protection device if required for its detection logic.
More recently, protective relay designs have been microprocessor based and provide multi-functional protection, monitoring, and control capabilities with multiple data communication ports; such relay designs are commonly referred to as a digital relay, a computer relay, or an intelligent electronic device (IED). Using existing techniques, testing each protection function of such IEDs presents a complicated task. Multiple simulations of normal, faulted, or abnormal power system conditions are required for the IED to uniquely respond with each individual protection function. For each response, an individual output contact must be dedicated for that function. To ensure that the IED responds with the proper logic of various protection functions, each function needs to be monitored individually and simultaneously by the test system. This generally requires a large number of available output contacts on the IED and a corresponding number of input monitoring points on the test system. Since this is neither economical nor practical, testing is relegated to a limited number of outputs and inputs for both IED and test system. In order to test all IED protective functions, a procedure of individually enabling a protective function and testing or rewiring of some output/input connections of the test system is needed. This procedure is both time-consuming and prone to error depending on familiarity with the IED and test system and the complication of the simulation required.
A new generation of microprocessor based intelligent electronic devices (IED) with high-speed peer-to-peer communications for protection and control is now becoming the standard in the electric power industry. Industry standard development projects through IEEE and IEC have developed and are nearing adoption of the UCA 2.0 and IEC 61850 communication standards. Both are in draft form but are considered to have been informally adopted by the industry as standards defining the communication protocol among IEDs. These IED devices incorporate the protocol set forth in the standards. Ultimately, the IEDs are designed to replace the exchange of status and control signals between them-previously based on individually wired binary outputs and inputs-with the exchange of data packets containing the status and control signals over a communication link, such as, for example, a direct serial link or over a local area network (LAN), or any other communication means available. Such IED devices cannot be tested with the existing state-of-the-art test systems. These devices require the development of new test solutions to determine functional performance.
Following existing techniques, the test system simulated different power system conditions using analog outputs to generate current and voltage waveforms, and individual relay outputs to simulate the status of power system apparatus like circuit breakers, and other logic and control signals to the IED under test. This required the individual wiring of the test system""s contact outputs to the monitored binary inputs of the IED under test. Conversely, to evaluate the performance of the IED under test, existing equipment and techniques require individually wiring each IED functional output to a monitored input of the test system. (FIG. 1)
Existing test systems are designed only to monitor the physical relay outputs of the IED under test and only to simulate power system apparatus status and control signals through their relay outputs, based on individual direct wiring between the IED under test and the test system. Therefore, prior art test systems simply cannot be used for the testing of communications-based IEDs.
Briefly, according to the present invention, a test device provides testing for testing power system protection, control, and monitoring, communication-based IEDs. Simulated power system conditions are applied to a device under test which in turn transmits status information back to the test device. Communications between the test device and the device or devices under test is had over a digital communications link such as a local area network. Individual point-to-point or hardwired connections are avoided through the use of the network link among the test device and the device(s) under test. The test device formats an output status to be transmitted into a data packet to the device under test, such that the test device simulates power system status of other virtual IEDs. The test device receives status information from the device(s) under test in response to both an applied analog voltage and current waveform and output status digital signals transmitted over the network links. The test device further performs automated test sequences based on the response of the device under test to the simulated power system conditions. Response to the test sequence is then compiled and utilized within the test device to perform power system simulation or IED performance evaluation.